1. Technical Field
The present invention relates to wireless communications, and more particularly, to a method of receiving a multimedia broadcast/multicast service (MBMS) in a cell-based wireless communication system.
2. Related Art
Similarly to a conventional cell broadcast service (CBS), a multimedia broadcast/multicast service (MBMS) simultaneously transmits a data packet in the same manner to a plurality of users. The CBS is a low-speed message-based service whereas the MBMS aims at high-speed multimedia data transmission. Further, the CBS is not based on an Internet protocol (IP) whereas the MBMS is based on IP multicast. If users satisfying a specific level exist in the same cell, necessary resources (or channels) transmitted to each user are shared so that a plurality of users can receive the same multimedia data. Therefore, the MBMS has an advantage in that radio resources can be more efficiently used and a multimedia service can be used at a low price from the perspective of the users.
The MBMS uses a common channel so that a plurality of user equipments (UEs) effectively receive data of one service. That is, regarding the data of one service, only one common channel is allocated instead of allocating a predetermined number of dedicated channels corresponding to the plurality of UEs which intend to receive the service in one cell. Since the plurality of UEs simultaneously receive the common channel, efficiency of radio resources increases.
The conventional MBMS service is provided in a single-carrier system. Herein, a carrier denotes one bandwidth and a center frequency. To provide various MBMS services to the same region, a hierarchical cell management method for providing different MBMS services over different frequency bands may be used. For example, when several cells having different frequencies are located in the same region, an MBMS service #1 may be transmitted from a first cell, and an MBMS service #2 may be transmitted from a second cell. In this case, there is a problem in that an MBMS UE located in the first cell cannot receive the MBMS service #2. This problem can be solved when the first cell reports information regarding the MBMS service #2 of the second cell to the UE.
However, when such a method applies to a multi-carrier or multi-cell system, an overhead caused by transmission of control information may occur. For example, it is assumed that a first carrier (or first cell) provides the MBMS service #1 and a second carrier (or second cell) does not provide any MBMS service in the same region. Even if the second carrier (or second cell) does not provide any MBMS service, when an additional control channel is transmitted for the MBMS service #1, an overhead caused by the control channel occurs. The greater the number of other carriers (or cells) providing the MBMS service, the greater the overhead. This implies an increase in the amount of control information that needs to be received for the MBMS by the UE, thereby consequently increasing a reception overhead of the UE receiving the MBMS. Accordingly, there is a need for a method of effectively receiving the MBMS in a multi-carrier system.